搜索结果：Fertility and sterility

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Cytoplasmic male sterility (CMS), a condition under which a plant is unable to produce functional pollen, is widespread among higher plants. CMS systems represent a valuable tool in the production of hybrid seed in self-pollinating crop species, including maize, rice, cotton, and a number of vegetable crops. Hybrids often exhibit heterosis, more commonly known as hybrid vigor, whereby hybrid progeny exhibit superior growth characteristics relative to either of the parental lines. CMS systems can be of considerable value in facilitating efficient hybrid seed production. There is growing interest in improving hybrid technology both to help supply food for the world's increasing population and to contribute to land conservation efforts. For example, the use of hybrid rice enabled China to reduce the total amount of land planted to rice from 36.5 Mha in 1975 to 30.5 Mha in 2000 while at the same time increasing total production from 128 to 189 million tons, representing a yield increase of 3.5 to 6.2 tons/ha (http://www.fao.org/rice2004). Understanding the molecular basis of CMS, as well as other hybrid production methods involving self-incompatibility and apomixis, is critical for continued improvements in hybrid technology. CMS is a maternally inherited trait that is often associated with unusual open reading frames (ORFs) found in mitochondrial genomes (Chase and Babay-Laughnan, 2004; Hanson and Bentolila, 2004). In many cases, it has been found that male fertility can be restored by nuclear-encoded fertility restorer (Rf) gene(s). CMS/Rf systems therefore are also of value in the study of interactions between nuclear and mitochondrial genomes. On the one hand, sterility results from mitochondrial genes causing cytoplasmic dysfunction, and on the other, fertility restoration relies on nuclear genes that suppress cytoplasmic dysfunction. CMS can arise spontaneously in breeding lines, as a result of wide crosses or the interspecific exchange of nuclear and cytoplasmic genomes, or following mutagenesis (Hanson and Bentolila, 2004). For example, CMS-WA (wild abortive) rice was developed in indica rice cultivars from a male-sterile plant found in a natural population of the wild rice Oryza rufipogon Griff. CMS-Boro II rice arose from a wide cross based on the cytoplasm of Chinsurah Boro II (O. sativa subsp indica) and the nucleus of Taichung 65 (subsp japonica). The well-known male-sterile Texas cytoplasm in maize arose spontaneously in a breeding line, and CMS-PET1 cytoplasm of sunflower arose from an interspecific cross between Helianthus petiolaris and H. annuus. There are a number of different types of CMS systems with distinct genetic features, both within and among different species, but key features that appear to be shared across different types are (1) CMS is associated with chimeric mitochondrial ORFs, and (2) fertility restoration is often associated with genes encoding pentatricopeptide repeat (PPR) proteins (Chase and Babay-Laughnan, 2004; Hanson and Bentolila, 2004). In this issue of The Plant Cell, Wang et al. (pages 676–687) describe details of the molecular basis of CMS and fertility restoration in the CMS-Boro II system in rice, which are likely to have far-reaching implications for CMS systems in general. First, the authors show that the mitochondrial orf79 associated with CMS-Boro II encodes a cytotoxic peptide responsible for CMS, and second, they show that two PPR proteins encoded by the Rf-1 locus in the Boro II system block the production of this cytotoxic peptide by distinct mechanisms (endonucleolytic cleavage and degradation of the dicistronic mRNA). In the early 1990s, several groups reported that rice CMS-Boro II is associated with an abnormal copy of the mitochondrial gene apt6 (Kadowaki et al., 1990; Iwabuchi et al., 1993) that produces aberrant mRNA transcripts containing an additional ORF named orf79 (Akagi et al., 1994). Interestingly, in a number of well-characterized systems, CMS is associated with alterations in promoter regions and portions of coding regions of mitochondrial ATP synthase subunit genes, which raises the possibility that impaired ATP synthase activity could be a causal factor in the disrupted pollen development in CMS lines in a number of species (Hanson and Bentolila, 2004). It is more often considered that transcription of unusual or aberrant ORFs is causally related to CMS, and it has been shown that CMS-associated mitochondrial ORFs encode proteins with cytotoxic properties in sunflower (Nakai et al., 1995) and Brassicaceae species (Duroc et al., 2005). However, it was unknown if CMS-Boro II resulted from incorrect translation of atp6 or from translation of downstream sequences including orf79. Akagi et al. (1994) found that orf79 encodes a predicted transmembrane protein with a novel C-terminal region and an N terminus showing similarity to the rice mitochondrial cytochrome oxidase subunit I. It was suspected that orf79 causes CMS in Boro II cytoplasm, but definitive proof has been lacking. Pollen Grains of a Normal Fertile Rice Line and orf79-Transgenic Rice Plants. Top, normal fertile rice line; middle, orf79-transgenic rice plants. Fertile pollen grains are darkly stained, and sterile grains are lightly stained. Bars = 50 μm. Bottom panel shows cosegregation of the orf79 transgene and male sterility (s) in transgenic plants. f, male-fertile. In addition, using immunoblot analysis, Wang et al. show that, despite the constitutive RNA expression of the gene, ORF79 protein accumulates specifically in the microspores of a CMS line but is absent in sporophytic tissues (as well as the microspores of fertility-restored plants). They propose that there may be a posttranslational regulatory mechanism that suppresses the accumulation of the protein, which could explain the genetic feature of gametophytic male sterility and why orf79 does not disrupt the development of sporophytic tissues. Wang et al. then sought to characterize the nature of the complex Rf1 chromosomal region and clarify the molecular mechanism underlying fertility restoration. The restoring allele Rf-1 is present in some indica rice lines, whereas most lines of the subspecies japonica carry a nonrestoring rf-1 allele. Previous research had shown that Rf-1 encodes a PPR protein that functions in fertility restoration of CMS-Boro II (Kazama and Toriyama, 2003; Akagi et al., 2004; Komori et al., 2004). Akagi et al. (2004) showed that Rf-1 is a complex locus containing multiple copies of genes encoding PPR proteins. One of the genes, Rf-1A, encoded a predicted PPR protein of 791 amino acids that contained a mitochondria-targeting signal and cosegregated with fertility restoration. This was the same gene cloned by Kazama and Toriyama (2003) (called PPR8-1) and Komori et al. (2004) (called PPR791) and thus has been considered to be the single gene responsible for fertility restoration. Akagi et al. (2004) also identified two other genes thought to be nonfunctional in fertility restoration: Rf-1B, which encoded a truncated protein that lacked a mitochondrial-transit signal, and Rf-1C, which encoded a protein of high similarity to Rf-1A but was outside of the crossover point of the experimental recombinants. Wang et al. used map-based cloning to sequence a 37-kb region surrounding Rf-1. They identified two genes that encode PPR proteins, called Rf1a and Rf1b, which were found by complementation testing to function in fertility restoration in this system. Rf1a corresponds to Rf1A/PPR8-1/PPR791 identified in previous studies, whereas Rf1b is another gene at this locus that has not been described previously. Wang et al. show that the RF1A and RF1B proteins both function to restore male fertility by blocking ORF79 production via somewhat different mechanisms. RF1A is shown to mediate endonucleolytic cleavage of the dicistronic atp6/orf79 mRNA at three major regions, each with multiple cleaving sites, whereas RF1B mediates degradation of atp6/orf79 mRNA with no detectable intermediates. RF1A function was found to be epistatic over RF1B, such that when both were present, atp6/orf79 mRNA was preferentially cleaved by RF1A, and the cleavage products were not susceptible to further degradation mediated by RF1B. The authors suggest that different fertility restorer lines may carry either or both functional copies of Rf1a and Rf1b, and the restorer lines in previous studies presumably did not carry a functional Rf1b allele. PPR proteins constitute a large family, with >400 members in Arabidopsis and rice that are thought to be RNA binding proteins involved in posttranscriptional processes (RNA processing and translation) in mitochondria and chloroplasts, but little data exist on the functions of individual proteins in this family (Lurin et al., 2004). Lurin et al. (2004) hypothesized that they function as sequence-specific adaptors for a variety of other RNA-associated proteins. This idea was supported by Schmitz-Linneweber et al. (2005), who showed that the maize PPR protein CRP1 influences expression of chloroplast genes through association with specific mRNAs, and Kotera et al. (2005), who showed that PPR proteins are involved in mRNA editing in chloroplasts. Bentolila et al. (2002) suggested an mRNA processing function for Rf PPR function after identifying the first Rf gene in petunia, which was found to encode the PPR protein Rf-PPR592. They observed that the presence of the restorer Rf-PPR592 led to a decrease in the gene product of the aberrant mitochondrial ORF pcf and concluded that Rf-PPR592 is likely involved in mediating a reduction in mRNA accumulation. Wang et al. provide definitive support for this hypothesis, showing that Rf PPR proteins participate both in endonucleolytic cleavage (RF1A) and degradation (RF1B) of specific mRNAs. They further show that RF1A functions to promote the editing of normal atp6 mRNA independently of its cleavage of dicistronic atp6/orf79 mRNA and role in fertility restoration and suggest that this may be its primary function. The results of Wang et al. have important implications for other CMS systems. For example, the A3 CMS system in sorghum has similar features with the CMS-Boro II system in rice: the mitochondrial CMS gene of sorghum, orf107, is similar to rice orf79 (Tang et al., 1996), and fertility restoration in sorghum is associated with the editing status of mitochondrial atp6 (Pring et al., 1999). In addition, previous work has suggested that Rf loci associated with fertility restoration in the genetically distinct rice CMS systems CMS-WA (Zhang et al., 2002) and CMS-HL (Liu et al., 2004) map to the same PPR gene cluster as the CMS-Boro II Rf-1 locus. Wang et al. hypothesize that a number of different genes within this PPR cluster have been recruited as fertility restorers with divergent molecular functions. Analyses of these clusters in other CMS systems are needed for a complete understanding of the evolution and molecular basis of CMS.

The effects of consanguineous marriages on couples' fertility and sterility were explored through an interview survey of 20 626 women, chosen randomly from the rural and urban areas of the North Arcot District of Tamil Nadu State. Qualified women investigators obtained relevant information about reproductive performances of all married women resident in well defined rural and urban samples chosen randomly from North Arcot District. For each marriage, a family pedigree was drawn, extending upwards to two earlier generations on both sides of each spouse, in order to determine the existence and type of consanguinity involved. Of marriages in rural areas, 46·9% were consanguineous, and in urban areas, 29·1%. In more than 80% of the consanguineous marriages, the spouses were first cousins or more closely related. The extent of primary and secondary sterility and the level of fertility were examined in relation to each type of consanguineous marriage with the duration of the marriage and the age of the woman. The frequency of primary sterility appeared to be lower in the consanguineous marriages compared to that in the non-consanguineous marriages. However, the differences were only marginal and only occasionally attained statistical significance. No trends were seen in the degree of consanguineous relationship, and there did not appear to be any association with the duration of marriage or the age of the woman. The frequencies of secondary sterility did not differ significantly in consanguineous marriages in either the rural or the urban areas. No consistent associations were observed with degree of relationship. There were no specific associations in terms of the duration of marriage or the age of the woman observed in the frequencies of secondary sterility. The mean levels of fertility were slightly raised among the consanguineous marriages and attained significance merely because of the large sample sizes involved. These findings are discussed and compared with relevant published work. Comparisons are made difficult because of paucity of data based on community studies, and also because great differences exist in the methodology adopted by various investigators. The findings from the present study seem to show that long-term inbreeding results in only marginal or non-significant effects on fertility of inbred populations.

In plants, male sterility can be caused either by mitochondrial genes with coupled nuclear genes or by nuclear genes alone; the resulting conditions are known as cytoplasmic male sterility (CMS) and genic male sterility (GMS), respectively. CMS and GMS facilitate hybrid seed production for many crops and thus allow breeders to harness yield gains associated with hybrid vigor (heterosis). In CMS, layers of interaction between mitochondrial and nuclear genes control its male specificity, occurrence, and restoration of fertility. Environment-sensitive GMS (EGMS) mutants may involve epigenetic control by noncoding RNAs and can revert to fertility under different growth conditions, making them useful breeding materials in the hybrid seed industry. Here, we review recent research on CMS and EGMS systems in crops, summarize general models of male sterility and fertility restoration, and discuss the evolutionary significance of these reproductive systems.

Cytoplasmic male sterility (CMS) is a maternally inherited trait that causes dysfunctions in pollen and anther development. CMS is caused by the interaction between nuclear and mitochondrial genomes. A product of a CMS-causing gene encoded by the mitochondrial genome affects mitochondrial function and the regulation of nuclear genes, leading to male sterility. In contrast, the RESTORER OF FERTILITY gene (Rf gene) in the nuclear genome suppresses the expression of the CMS-causing gene and restores male fertility. An alloplasmic CMS line is often bred as a result of nuclear substitution, which causes the removal of functional Rf genes and allows the expression of a CMS-causing gene in mitochondria. The CMS/Rf system is an excellent model for understanding the genetic interactions and cooperative functions of mitochondrial and nuclear genomes in plants, and is also an agronomically important trait for hybrid seed production. In this review article, pollen and anther phenotypes of CMS, CMS-associated mitochondrial genes, Rf genes, and the mechanism that causes pollen abortion and its agronomical application for rice are described.

Curious about the geographical distribution of publications in reproductive medicine, we compared the numbers of publications in Human Reproduction (HR) and Fertility and Sterility (F&S). The annual number of publications from the individual countries was obtained by searching the Medline database using the internet provider PubMed. The data were analysed and normalized to population size, gross domestic product (GDP) and total number of Medline publications. The 8511 publications of both journals in the 1990s came from 56 countries. The number of publications per year was increasing in HR and remained constant in F&S. In absolute numbers, the UK produced the most publications in HR (21%) and the USA in F&S (45%) as well as in both journals together (28%). Relatively, Israel was the most productive country per million inhabitants (8.4 +/- 2.1 publications/year), per billion US dollars GDP (0.85 +/- 0.21 publications/year) and per 1000 Medline publications (15 +/- 4 publications/year). Europe was the most productive world region in absolute numbers (54%) and Australia/New Zealand in relative numbers per million inhabitants and per 1000 billion US dollars GDP. Almost 87% of all publications in HR and F&S came from the 18 countries with a GDP per capita of >10 000 US dollars. In conclusion, the geographical distribution of publications in HR and F&S follows the pattern of the distribution of publications in general biomedical research. Most publications come from affluent countries. Although the USA and the UK appear to be the most productive countries in absolute numbers, smaller affluent countries like Israel and Belgium are more productive when the numbers are normalized to population or GDP.

Hybrid wheat varieties give higher yields than conventional lines but are difficult to produce due to a lack of effective control of male fertility in breeding lines. One promising system involves the Rf1 and Rf3 genes that restore fertility of wheat plants carrying Triticum timopheevii-type cytoplasmic male sterility (T-CMS). Here, by genetic mapping and comparative sequence analyses, we identify Rf1 and Rf3 candidates that can restore normal pollen production in transgenic wheat plants carrying T-CMS. We show that Rf1 and Rf3 bind to the mitochondrial orf279 transcript and induce cleavage, preventing expression of the CMS trait. The identification of restorer genes in wheat is an important step towards the development of hybrid wheat varieties based on a CMS-Rf system. The characterisation of their mode of action brings insights into the molecular basis of CMS and fertility restoration in plants.

Summary. Immune sera produced against bull semen in cattle and against washed bull spermatozoa in rabbits caused an antifertility effect (fertilization failure or possibly early embryonic death), when used to treat the bull semen prior to insemination of heifers. Fertilization was prevented in rabbits inseminated with semen treated with cattle antirabbit semen serum. Normal fertility occurred in both species when the semen was treated with normal sera. Fertilization was prevented in rabbits inseminated with semen treated with the gamma-globulin fraction of the immune serum, but not with the gamma-globulin fraction of the normal serum. Absorption of the rabbit anti-bull-sperm sera and the cattle antirabbit-semen sera with the erythrocytes of bulls and male rabbits, respectively, failed to remove the sperm agglutinins or the antifertility effect of these antisera. Absorption of these sera with the appropriate washed spermatozoa removed the agglutinins and the antifertility effect. Antisera to erythrocytes did not possess either sperm agglutinins or the antifertility effect when used to treat bull or rabbit semen. Similarly, antisera to semen or washed spermatozoa had little or no specific agglutinins against erythrocytes. These results indicate that antibodies against semen or washed spermatozoa can prevent fertilization, or may cause embryonic death. Further, they indicate the absence of cross-reactivity between the antigens of either seminal plasma or spermatozoa and erythrocytes.

The plant mitochondrial genome is characterized by a complex, multipartite structure. In cytoplasmic male-sterile (CMS) common bean, the sterility-inducing mitochondrial configuration maps as three autonomous DNA molecules, one containing the sterility-associated sequence pvs-or f 239. We constructed a physical map of the mitochondrial genome from the direct progenitors to the CMS cytoplasm and have shown that it maps as a single, circular master configuration. With long-exposure autoradiography of DNA gel blots and polymerase chain reaction analysis, we demonstrate that the three-molecule CMS-associated configuration was present at unusually low copy number within the progenitor genome and that the progenitor form was present substoichiometrically within the genome of the CMS line. Furthermore, upon spontaneous reversion to fertility, the progenitor genomic configuration as well as the molecule containing the pvs-or f 239 sterility-associated sequence were both maintained at substoichiometric levels within the revertant genome. In vitro mitochondrial incubation results demonstrated that the genomic shift of the pvs-or f 239-containing molecule to substoichiometric levels upon spontaneous reversion was a reversible phenomenon. Moreover, we demonstrate that substoichiometric forms, apparently silent with regard to gene expression, are transcriptionally and translationally active once amplified. Thus, copy number suppression may serve as an effective means of regulating gene expression in plant mitochondria.

Meiosis is an event of high evolutionary stability which culminates in a reduction of chromosome number. The normal and harmonious course of meiosis ensures gamete viability. The cytologic events of gametogenesis are controlled by a large number of genes that act from premeiotic to postmeiotic mitosis. Mutations in these genes cause anomalies that may impair fertility, and many abnormalities affecting plant fertility or causing total male sterility have been detected during the evaluation of meiotic behavior in some species. Some of these abnormalities have been frequently described in the literature, while others have not been previously reported. The most frequent abnormalities found in the species analyzed were irregular chromosome segregation, cytomixis, chromosome stickiness, mixoploidy, chromosome fragmentation, syncyte formation, abnormal spindles, and failure of cytokinesis. Uncommon abnormalities, such as chromosome elimination during microsporogenesis, were found in one species. Original meiotic mutations affecting different steps of meiosis were also observed in these species, especially in maize, Paspalum and soybean. Some mutants present characteristics that may be exploited successfully in breeding programs because they cause total male sterility.

An ideal method of controlling conception, it has been said, must be harmless and convenient and must not offend taste or esthetic sensibilities; it should not affect sensation, it should be easily applied and it should be cheap and safe. The Ogino-Knaus method, it is claimed, fulfils all these requirements, with the possible exception of a certain amount of inconvenience. Periods of abstinence are required, but this is probably not a serious difficulty. Furthermore, the method has the approval of the church and the synagogue. Whether it is really safe is still a matter of discussion. The authors claim it to be so in 90 per cent of cases, as large a percentage of effectiveness as has been demonstrated for any of the mechanical and chemical devices available. The failures are attributed to very irregular menstruation, poor general health, disobedience and inadequate attention on the part of the women to

Summary Heifers were immunized with rabbit semen. The immune sera (IS) from them, in high concentrations, caused tail-tail agglutination of rabbit sperm in contrast to a head-head type produced by normal sera (NS). Diluted rabbit semen (same concentration for each trial) was mixed with NS and IS approximately 15 min before being used for insemination. Normal serum did not affect fertilization. High concentrations of IS prevented fertilization but the fertilization rate increased as lower concentrations were used (173 females studied). Embryo survival percentage was estimated in the NS and IS groups by a comparison of the number of fertilized ova in a random sample of females killed at 28 hours after insemination with the number of surviving fetuses in a comparable group of females at 28 days. The average embryo survival percentage for 58 IS females was 38.2 compared to 53.1 for 59 NS females. The loss of whole litters was much more common in the IS group (23 females out of 58) than it was in the NS group (3 females out of 59). Resorbing embryos or placental sites were found in 17 of the 23 IS females. A significantly greater amount (P < 0.005) of embryonic death occurred in the IS group. The mechanism by which the antibodies caused fertilization failure and embryonic death is not known. The effect on fertility could not be explained on the basis of the gross amount of sperm agglutination or any marked interference with sperm motility.